Papua New Guinea government is ruled illegal

Police erected road blocks in the capital of Papua New Guinea on Monday before a court ruled the government was illegal and ordered that Sir Michael Somare, toppled while receiving medical treatment overseas, be reinstated as prime minister.

PNG media reported the politically unstable South Pacific island nation's Supreme Court ruled that the government led by Peter O'Neill had no right to take office while Somare was out of the country receiving treatment for a heart ailment.

Residents said all was quiet despite the security measures taken by police, who feared protests, to protect the courthouse and other areas of the capital, Port Moresby.

The fate of O'Neill's government remained unclear, with media reporting that the parliament again voted him in as prime minister after the court's ruling and that he was headed to government house to be sworn in once again.

PNG's Commissioner of Police Tom Kulunga called for calm in the resource-rich nation.

"I call upon all leaders ... to exercise caution, restraint and act responsibly. What you decide to do now can and will determine the future of Papua New Guinea," he said.

PNG has a history of turbulent politics. Governments have been toppled as MPs frequently change party allegiances, but its "golden goose" resource sector has largely been left unhindered by the turmoil.

US oil giant ExxonMobil leads a consortium building the country's biggest-ever resource project, a $15.7 billion liquefied natural gas project due to come on stream in 2014. The LNG project is expected to produce 6.6 million tonnes per annum and could see GDP increase by 20 per cent.

Despite PNG's reserves of gold and gas, the majority of its seven million people live subsistence lifestyles on the sides of jungle-clad mountains. Bloody tribal wars are common, with the nation splintered into more than 800 language groups.

Somare, 75, was PNG's longest-serving prime minister, affectionately known as "the Chief" after leading the country to independence in 1973, and is regarded as the elder statesmen of the South Pacific.

The court ruled that Somare's absence overseas in Singapore for five months this year did not mean he had vacated the prime ministership, PNG media reported. The court could not be reached for immediate comment. O'Neill took office in August.

"The court ruled 3 to 2 that there was no vacancy," said National Broadcasting Corp reporter Mulai Robby.

Radio New Zealand International (RNZI) reported from Port Moresby that the court ruled the parliamentary vote electing O'Neill as prime minister was illegal.

However, the O'Neill government passed a series of amendments in parliament on Monday to legalise his elevation to the top job, said RNZI. One new law made the dumping of Sir Michael legal, specifying that a prime minister can be dismissed if absent from the nation for more than three months, it said.